Ecology Abstracts
|
Pending Publishing Permission
Predicting habitat-specific carrying capacity (K) and incorporating multiple data types into an integrative population model (IPM) to support sea otter management Tim Tinker and Lilian Carswell, US Geological Survey, Western Ecological Research Center, Nhydra Ecological Research Services Full Abstract
The past 20 years have seen enormous advances in our understanding of sea otter biology and ecology, together with insights into specific threats to sea otter recovery, including infectious disease, resource limitation and predation mortality. While southern sea otters have gradually increased in abundance to the threshold where de-listing (under the U.S. Endangered Species Act) may be considered, the current distribution represents only a fraction of the historic distribution and range expansion has stalled, apparently as a result of ongoing threats. Resource managers face two general challenges: 1) how can we predict the optimum sustainable population (OSP) for southern sea otters as a realistic target for management, accounting for spatial variation in habitat quality and localized carrying capacity; and 2) what specific factors and threats are most important in terms of limiting recovery to OSP in different regions (or, as a corollary, what management actions will have the greatest effect on recovery)? We present a habitat-based estimate of carrying capacity (K) for southern sea otters. We then combine spatially-varying K estimates with a comprehensive array of available data sets to produce an Integrative Population Model, or IPM, that can help address emerging conservation challenges. We briefly explain the models, and then provide a demonstration of the IPM in action. |
Pending Publishing Permission
Top-level carnivores linked across the marine/terrestrial interface: sea otter haul-outs offer a unique foraging opportunity to brown bears Daniel Monson, United States Geological Survey (USGS) Full Abstract
Commercial exploitation in the 18th and 19th centuries eliminated sea otters from most of their range including the coastline of what is now Katmai National Park and Preserve (KATM). However, a remnant sea otter population remained north of Cape Douglas, and by the early 1990’s sea otters had expanded their range into KATM with the area supporting ~1000 animals. Sea otter abundance has increased approximately seven-fold since the early 1990’s and now appears to be approaching carrying capacity. Sea otters along the KATM coast utilize offshore islands as haul out sites where brown bears are also commonly found. Since 2006, we have collected sea otter carcasses from the offshore islands along the KATM coast with most carcasses showing signs of being consumed by brown bears. Population models using the carcass collections as representative sea otter age-at-death data suggest the population should be declining, which contrasts with sea otter surveys that do not suggest a decline over a similar time frame. We deployed remote cameras on two offshore islands and documented brown bears actively preying on both sea otters and harbor seals. We conclude that 1) brown bears occupy offshore islands along the KATM coast to hunt marine mammals, not just to scavenge carcasses, and 2) brown bear predation causes more prime age otter mortality than expected in a typical otter age-at-death distribution, confusing interpretation of population models based on such data. This study highlights a previously under recognized interaction between a top-level marine and terrestrial predator. Future work will focus on the direct and indirect effects these top-level predators have on each other and the intertidal community that connects them. |
Where carnivores clash: evidence of competition—prey-shifting by brown bears during a period of sea otter recovery Heather Coletti, National Park Service Watch Video (Login required) Full Abstract
Sea otters are an important component of the northeastern Pacific nearshore ecosystem because when present, they have dramatic effects on nearshore subtidal and intertidal community structure and dynamics. However, commercial exploitation in the 18th and 19th centuries eliminated sea otters from the vast majority of their range, allowing their invertebrate prey populations to proliferate. Prior to substantial recovery of the sea otter population along the coast of Katmai National Park and Preserve within southcentral Alaska, brown bears utilized the abundant intertidal clam resources available there. However, in recent decades, the Katmai sea otter population has increased by approximately seven fold. In the early 1990’s, brown bears along the Katmai coast were commonly observed foraging on clams in the intertidal. At that time, the Katmai sea otter population was just beginning its recovery and was estimated to be less than 1000 animals. By 2006 the sea otter population had grown to approximately 7000 animals and appears to have peaked or stabilized, with clams being their primary prey. Since 2006, sea otter energy recovery rates have declined suggesting the otter population is approaching carrying capacity. In contrast, brown bears monitored from 2015-2017 showed almost no sign of utilizing intertidal clam resources. Our results suggest sea otters out-competed bears for intertidal resources by reducing clam abundance (and thus the calories bears could consume per unit time) to the point where most bears switched to other resources. With sea otters restored to the ecosystem, indirect effects on the nearshore community likely include increased canopy and understory kelps, which could enhance salmon smolt rearing habitat and positively influence availability of salmon, the single most important food resource of Katmai brown bears. This work adds to a growing body of evidence for the cascading ecosystem effects of top-level carnivores and highlights interactions between top-level marine and terrestrial predators that have not been documented elsewhere. |
|
Pending Publishing Permission
Long-term trends for sea otters on the Pacific Northwest coast from archeological remains and traditional knowledge: ecological and indigenous histories before the maritime fur trade Iain McKechnie and Anne Salomon, University of Victoria and Simon Fraser University Full Abstract
The relationship between humans and sea otters, two well-documented keystone predators occupying the north Pacific rim, has spanned millennia yet their interactions over this time remain unresolved despite their profound ecological and social-cultural significance. Here we present a meta-analysis of zooarchaeological data from the Pacific Northwest Coast that pieces together existing archaeological information about the spatial and temporal variation in these keystone interactions through deep time to gain a better understanding of ecological and socio-cultural implications of these dynamics in the past, address the symptoms of sliding baselines, and ultimately inform future conservation and management strategies. |
Pending Publishing Permission
#TeamOpenCoast or #TeamEstuary? : The costs and benefits of two key sea otter habitats Jessica Fujii, Monterey Bay Aquarium Full Abstract
Despite traditionally being associated with kelp forest habitats, sea otters also populate soft-sediment bays, lagoons, and estuaries within their current ranges. These habitats can offer different benefits and constraints to individuals, such as prey availability and diversity, survival risks and access to resting and feeding areas. By improving our understanding of how sea otters adapt to and use these different habitats, we can better predict how sea otters will respond to potential novel environments as they expand their population range in California. We compare sea otter behavior (such as diet, forage patterns, hauling-out frequency, home range, and survival) from residents monitored in Elkhorn Slough (estuary habitat) and Monterey and Big Sur (open coast habitat) and how it may relate to environmental differences (sea surface temperature, habitat features (tidal change, depth, land access)). We found that sea otters residing in Elkhorn slough had lower diet diversity, drastically smaller home range sizes, and spent more time hauled out. Although Elkhorn Slough provided protection from sharks, calmer sea conditions, and warmer water, their mean annual survival rate did not differ significantly from open coast sea otters. Other attributes commonly associated with density dependence (time spent foraging and length of pup dependency) followed the same patterns in the estuary population as previously observed open coast habitats. Our results suggest that both habitat types can play an important role in future range expansion |
Pending Publishing Permission
Revisiting the role of southern sea otters in California kelp forests Sophia Lyon, US Geological Survey and UC Santa Cruz Long Marine Lab Full Abstract
The role of sea otters as a keystone predator in kelp forest ecosystems has often been described, but recent evidence suggests that their impacts on prey populations may be mediated by the presence or absence of other predators. Between 2013 and 2015, several species of sea stars experienced widespread declines (from California and Alaska) due to viral disease. This wasting disease caused local extinctions of the predatory sea star Pycnopodia helianthoides: around the same time, urchin populations increased sharply in central California (possibly in response to the loss of Pycnopodia) leading to reductions in kelp and the emergence of urchin barrens. This massive perturbation – the wholescale removal of one predator – provided an “opportunistic experiment”, which we capitalized on to evaluate the possible interactive role of sea otters and sea stars in controlling urchins. A second objective was to investigate how individual diet specialization in sea otters might mediate their response to increased urchin abundance. In June of 2016, twenty-six otters were tagged and instrumented with VHF radio transmitters and time depth recorders and have been monitored daily to collect observational data on survival, reproduction, habitat use, diet and foraging behavior. We compare results to data collected in previous studies along the Monterey Peninsula, to determine whether and how sea otters have altered their behavior in response to the shift in prey dynamics. Our study is combined with scuba-based experiments to measure urchin mortality rates under different predator regimes, and to test how urchin quality affects likelihood of selection by sea otter predators. Using the combined data, we will test two hypotheses: 1) sea otters and Pycnopodia play complementary roles in controlling herbivores, and 2) adaptive responses by sea otters can buffer the system from the loss of sea stars. We present preliminary results from the first 2.5 years of the study. |
|
Sea otter diet composition with respect to recolonization, demographic and seasonal patterns in southern southeast Alaska Nicole LaRoche, University of Alaska Fairbanks Watch Video (Login required) Full Abstract
Until translocation efforts in the 1960s, sea otters (Enhydra lutris) were absent from Southeast Alaska due to extirpation from the fur trade in the 18th and 19th centuries. About 400 sea otters were reintroduced to six Southeast Alaska locations including two sites near Prince of Wales (POW) Island in southern Southeast Alaska. The most recent US Fish and Wildlife Service population count, completed in 2012, estimates that 25,000 sea otters inhabit Southeast Alaska. Previous foraging studies throughout the sea otter range have shown that sea otters will reduce invertebrate prey biomass when recolonizing an area. Foraging data were collected around the west coast of POW to determine diet composition. Sites were selected according to time-since-recolonization. A total of 3,372 foraging dives were recorded during May-August 2018. Across all sites, sea otter diet was overwhelmingly composed of clams (68% of total biomass). Sea otter diets were analyzed with respect to age, sex, seasonality, and inhabitance duration. The next step in this study includes macronutrient analysis and 13C/15N stable isotope analysis of sea otter prey to understand how Southeast Alaska sea otters meet their energetic needs compared to other sea otter populations and gain a better understanding of seasonal diet shifts. The results of this study will aid in future management of shellfisheries, subsistence hunting, and co-management of a protected species by providing quantitative data for stakeholders. This work is a part of a large-scale project examining how the recovery of sea otters structures nearshore marine ecosystems, provides ecosystem services, and affects community sustainability |
Velocity of community shift and alternative kelp forest states: how long-term subtidal monitoring can focus dialogue surrounding nearshore conservation and management
Zachary Randell, Oregon State University Watch Video (Login required) Full Abstract
Since 1980 biologists with the US Geological Survey, UC Santa Cruz, and the US Fish and Wildlife Service have biannually sampled six monitoring stations in the nearshore subtidal around San Nicolas Island (SNI), CA. This ongoing program has captured decadal periodicity (e.g., ENSO events, PDO), and the permanent sampling locations allow for a spatially explicit examination of how temporal dynamics vary around the island. However, the timeseries is more than just a record of the nearshore subtidal around SNI—it is a test of both our (1) empirical conceptualizations of how kelp forest communities are structured, and (2) our theoretical predictions for how ecosystems with one or more stable attractor change over time. Here we examine broad patterns of temporal dynamics, and we relate those kelp forest community dynamics to the physical substrate comprising the permanent sampling locations. To test predictions of dynamical systems theory, we relate velocities of community shift to the underlying Potential landscape comprising each transect. We present evidence of three alternative kelp forest states—deforested urchin barrens, a mixture of urchins and macroalgae, and macroalgae exclusive—and we examine how the stability and resilience of these respective states vary given local and broad scale factors, including the presence of the translocated sea otter population. By exploring how temporal community dynamics are modified by local factors, we have built a framework to think about the selection of nearshore subtidal locations that receive conservation and management attention. Specifically, we can focus attention towards nearshore subtidal locations that have greatest potential for exhibiting desired community structure, i.e., locations with the greatest potential for exhibiting stable macroalgae populations through time. |
The complex role of sea otters in southeast Alaska Ginny Eckert, University of Alaska Fairbanks Watch Video (Login required) Full Abstract
Sea otters were exterminated from Southeast Alaska during the 19th century maritime fur trade, but after reintroduction in the 1960’s, their population grew exponentially and at last count in 2011 included over 25,000 animals. The extirpation of sea otters and subsequent successful return has resulted in ecosystem changes in a wide variety of marine habitats and consequent changes in human behavior. Humans compete with sea otters for commercial and subsistence shellfish and coastal Alaska Native people harvest sea otters. Our social-ecological research documents patterns in sea otter harvest and declines in commercial and subsistence shellfish that correspond with decreases in food security in areas with abundant sea otters. On the other hand, sea otters are ecologically important as keystone species with ecosystem benefits in marine habitats including kelp forest and likely eelgrass meadows. We are investigating the trophic connections and role of disturbance of sea otters in eelgrass meadows, the role of eelgrass as nursery habitat for juvenile fish/shellfish and in sequestering carbon to ameliorate increasing atmospheric CO2. By developing a broader understanding of the social and ecological context of sea otters in Southeast Alaska, we may be more effective in appreciating the complex role of sea otters and bringing this information into the local and regional decision making process. |
|
Pending Publishing Permission
Sea otter recolonization associated with regional increase in kelp forest canopy Tom W. Bell, University of Alaska South East Full Abstract
Giant kelp (Macrocystis pyrifera) is a canopy forming foundation species that creates dense forests along shallow rocky reefs and provides energy and structure for a vibrant ecosystem. Sea otters (Enhydra lutris) are a keystone predator and serve as an important link in a trophic cascade by reducing herbivore pressure. Sea otters were reintroduced to SE Alaska and began to colonize Sitka Sound in the late-1970’s. There is anecdotal evidence of increased giant kelp in the sound in recent decades, following the collapse of the red urchin (Mesocentrotus franciscanus) fishery, an important kelp herbivore. To investigate the potential role otters played in this regional expansion of giant kelp, we used Landsat satellite imagery to construct a time series (1984–2018) of canopy biomass in both Sitka and Monterey, CA, where otters have had a prolonged presence. Sitka showed a significant positive increase in annual maximum kelp biomass while Monterey showed no significant trend. In Sitka there were increases in kelp area added concurrent with increases in otters, while Monterey showed little increase in new kelp area. It appears that increased otter predation on kelp herbivores in Sitka induced an ecosystem state shift to canopy forming kelps. We demonstrate a non-linear functional response between otter abundance and giant kelp canopy cover, with rapid but asymptotic increases occurring soon after otter recolonization. Our findings establish a foundation for large-scale study of the spatial patterns of kelp forest state shifts and sea otter recolonizations across SE Alaska. |